Semiconductor light emitting devices, such as light emitting diodes and laser diodes, can be obtained by forming a light emitting layer on a sapphire substrate or a GaN-based substrate. This substrate becomes unnecessary once the light emitting layer is formed. The light emitting layer is stable on the substrate, and therefore, the substrate is not removed but used as a part of the semiconductor light emitting element. As such, a transparent material is used for the substrate.
In semiconductor light emitting elements, a reduction in thickness of the substrate reduces loss of light which leaks from a side surface of the substrate. Thus, a reduction in substrate thickness is a way to be close to surface emitting.
On the other hand, a reduction in substrate thickness reduces the mechanical strength of the substrate, and as a result, the substrate may be cracked and the yield may be decreased. As a solution to this problem, a technique is provided in which a light emitting layer is formed on a substrate, fixed to an electrode, and then detached from the substrate using laser irradiation (see Patent Document 1).
There is also a technique in which a substrate is attached to another substrate using a double-faced tape; air bubbles at the attached portion are removed; and the thickness of the substrate is reduced without causing any cracks in the substrate (see Patent Document 2).    Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2006-128659    Patent Document 2: Japanese Laid-Open Patent Application Publication No. 2002-158193